Synchronous motor



BEST AVNL BLE COW V. A. FYNN Sept. 14, 1926. 1,599,760

SYNCHRONOUS MOTOR Filed April 4, 1924 36 enables the field current of the exciter to Patented Sept. 14, 1926. BEST VAiLABLE GDP;

VALEBE ALFRED FYNN, OF ST. LOUIS, MISSOURI.

SYNCHBONOUS MOTOR.

Application filed April 4,

My invention relates to the starting and operation of dynamo-electric machines n which a revolving field of more or less uniform magnitude is produced at least during the starting period and which derive their excitation from an exciter not integral with the machine although it may be driven.

thereby. It also relates to the operation of single-phase machines excited inthe manner stated andmore particularly it relates to means for utilizing an ordinary direct current exciter' for the purpose of improving the starting performance or the operation or both the starting and the operation of the synchronous machine with which said exciter co-operates. v p

The objects and features of'this invention will appear from the detail description taken in connection with the accompanying drawings and will be pointed outin the claims.

In the accompanyingdiagrammatic drawings, Fig. 1 shows the invention as applied to a two-pole three-phase synchronous induction motor and a two-pole diredt current exciter, Figs. 2 to 9, inclusive, are explanatory diagrams. q

Referring to Fig. 1, the polyphase synchronous induction motor carries a threephase winding 8 on its stator, which winding'is connected to the supply 2, 3, 4 through the variable ratio transformers 5, 6, 7. The secondary member of the motor, mounted on the shaft 19, carries a squirrel cage 11 and a two-phase winding 9, 10 connected to the sliprings 12, 13, 14 also carried by the shaft 19. The two-pole direct current exciter has an armature 34 mounted on the shaft 26 and a stationary field structure provided with the usual exciting winding connected tothe stationary brushes 32, 33 co-operating with the commutator attached to the winding on the armature 34. Anadjust'able resistance be regulated. This exciter is driven by the synchronous polyphasemotor through' the gear wheels :20, 42 of equal pitch diameter.

' Also co-operating with the commutator of the exciter is a pair of movable brushes'30, 31 insulatingly held in a brush support or rocker mounted on a sleeve 29 which is free to revolve on the shaft 26 of the exciter. This sleeve insulatingly carries the sliprings 27, 28 to which the brushes 30,31 are connected and has keyed to it a gear wheel engaging with the gear wheel 24 through the intermediate gear wheel 43. The gear 1924. Serial No. 704,092.

wheel 24 is of same pitch diameter as 25 and is carried by the middle element of a differential gear. One side element of this differential is mounted on the shaft 22 and driven by the motor shaft 19 through the gear wheels 20, 21 at the same speed as 19. The other side element of thediflerential is mounted on the shaft 42'and driven by the auxiliary synchronous two-pole motor 41 connected to the supply 2, 3, 4 through the two-pole phase regulator 37 provided with three movable contacts 38, 39, 40. When these contacts, which are normally spaced by 120 degrees, rest on the winding 37 of the phase regulator, the motor 41 is connected to the supply. The position of these contacts relatively to the points at which 37 is connected to thesupply determines the phase of the voltages impressed on 41 with rela tion to the phase of the supply voltages. The brush 31 co-operating with the commutator, of the exciter is connected to the sec-' ondary motor-windings .9 and 10 through the sliprings 28 and 13 and the brushes 00- operating with these sliprings; The brush -30 is connected to the secondary motor winding '9 through-thesliprings 27 .and 14 and the adjustable resistance 16; This brush is also connected to the secondary motorwinding 10 through the sliprings 27 and 12 and the adjustable resistance 15. The sliprings 13, 14, which means the secondary motor 7 winding 9, ca nbe shunted and shortcircuited, by the adjustable resistance 17. The slip rings 12, 13, which means the secondary -'inotor winding 10, can be shunted and shortcircuited' by the adjustable resistance 18.

I When the rotor of the synchronous motor revolves clockwise, -as-seen from that end of the shaft 19 which does not carry the gear wheel 20, then the exciter armature 34 and the shaft 22 of the differential revolve counterclockwise. Under these conditions the auxiliary motor 41 should drive .the shaft 42 of the'difi'erential in a clockwise direction. When the intermediate gear wheel 43 is used between the gear wheels 24 and 25-, then the brushes 30, 31 will revolve clockwise, or against the rotation of the commutator of the exciter, when the speed of the auxiliary motor is greater than that of the main motor and' vice versa. \Vhen' the 4 speeds of these two motors are the same then just like an ordinary squirrel cage or slipring polyphase induction motor. squirrel cage is provided and its resistance is low, the resistances 17, 18 are disconnected and the motor started with a terminal voltage below the normal, the reduction being secured by means of the variable ratio transformers 5, 6, 7 It is then preferred to give the resistances 15, 16 a high value at Starting or to entirely interrupt the circuit of the brushes 30, 31 at that time.

If the resistance of the squirrel cage is high enough or if it is entirely omitted,

.then the full terminal voltage may be impressed on the motor even when atrest and the machine brought to near synchronism by I shunting and finally shortcircuiting the secondary windings 9 and 10 by means of the resistances 17, 18. lVhenever the synchronous motor is of an appreciable size it is preferredto reduce the current through the brushes 30, 31 to a negligible value during the starting operation with a view to sparing the commutator of the exciter, When the motor is a small one the induction motor torque producing currents induced in the WlIldIIlgS.

9 and 10 at starting can be allowed to close over the brushes 30, 31 and the commutator of the exciter, in which case the resistances 17, 18 may be dispensed with. Their use is, however, preferred in most cases.

The auxiliarymotor 41 may be started before the main motor is started or it can be started later or concurrently with the main motor. If started first it will drive the brushes 30, 31 atsynchronous speed as long as shaft 19 is at rest. As the'main motor speeds up the speed of the brushes 30, 31 will diminish and become zero when the main motor has reached synchronism. As

' 31 and this voltage will be of slip frequency in so far as the main motor is concerned.

The magnitude of this slip frequency voltage is independent of the speed of the brushes 30, 31 and only depends on the speed of the exciter armature 34 and on the avail able exciting flux. Thefrequency of this slip frequency voltage depends on the speed of the brushes 30, '31 anc is independent of the speed of the exciter armature; it becomes- BEST AVAlLABLE COP:

the latter or in other words, to control its so doing I impress on the secondary wind ings 9, 10, or on one of them, an alternating voltage of slip frequency. ,If the phase of 'this voltage is properly chosen then I can secure a strictly unidirectional pulsating synchronizing torque which-will bring the main motor into step with more than full load torque, or I can secure a substantially unidirectional synchonizing torque by a somewhat'difl'erent phase setting. When but one of the windings 9 or 10 is connected to the brushes 30, 31 for synchronizing then the phase of the slip frequency voltage availv able at said brushes must be chosen with reference to the phase of the voltage generated in whichever secondary winding is being used. If both secondary windings 9 and 10'are used for synchronizing, then the phase of the slip frequency voltage is chosen with reference to the phaseofthe resultantsof the voltages generated in each of the secondary 4 windm p After the machine is m synchromsm, I can control its compounding characteristic. byv

adjusting the position of the brushes 30, 31 on the'commutator of the exciter for instance, with reference to the stationary brushes 32, 33 co-operating with the same exciter. To change the phase of the slip frequencyvoltage appearing at the brushes 30, 31 at subchronous speeds, or to change the position of said brushes on the commutator/of the exeiter' whe the main motor runs. at synchronous s ed, 1 can change the'phase of the voltages impressed on the auxiliary motor 41 by. displacing the movable contacts 38 .39, 40 of the phase regulator 37. A crude way of achieving the same result is to momentarily interrupt the connections between the auxiliary motor and the supply. Another way is to displace the field structure 35 of the exciter. I

The compounding characteristic can be very readily adjusted in case both secondary windings 9 and 10 are used by changing the ratio of the unidirectionalampereturns in said windings, for instance by means of the resistances 15, 16. f Just how the brushes 30,31 should be set in order .to obtain .a certain compounding characteristic or just how the phase of the synchronizing voltage, shouldbe chosen in order to secure the desired synchronizing torque can be readily explained with thehelp of Figs. 2 to 9, inclusive. a

Fig. 1 have been omitted. It is assumed that the flux F set up by the polyphase currents in the primary of the main motor revolves clockwise at slip frequency, while the. rotor of said motor is stationary. This is the same as if .F revolved synchronously and the rotor rotated in the same direction at synchronous minus the slip speed. The conditions to be considered are those obtaining very near synchi'onism, say at no-load. The exciter armature is supposed to revolve counterclockwise, as in Fig. 1, and the exciting flux E is directed as shown by the ar row within thefield pole 35 of the excitcr.

The voltage generated in 9 by rotation of F is a it is ofslip frequency. The voltage '0, appearing at the brushes 30, 31 which are supposed to revolve clockwise at slip fre-- quency, as in Fig. 1, is of same frequencyas e,. In order to secureia strictly unidirectional synchronizing torque e 'must be of same phase and direction as 6,. In other words, e must be zero when 6, is zero and at its positive maximum when? is at its .positive maximum. Whenthe axis of F coincides with that of 9, as in Fig. 2, then 6, is Zero. So that e may be zero at the same time, theaxis of the-brushes 30, 31 must concurrently coincide with thea'xis of the exciter exciting flux. Whether the brush 30 is to be connectedto-the lower or the upper terminal of 9 is settled by Fig. 3. After a movement'through 90'electrical degrees, F g and the brushes '30, 31 will occupy the posi-:

. tions shown in Fig. 3. Under these conditions the voltage generated in 9 by F would have the distribution-shown in Fig. 3 by full andempty circles,-zthe full circles or dots indicating. downwardly and the empty circles indicating upwardly directed voltage or current. If 9 were shortcircuited it would produce a clockwise or positive torque with F. The brushes 30, 31 must be connected to send a current into 9 which will yield a positive torque with F. The direction of the voltage and current produced in 34 by its counterclockwise rotation. within E is indicated by full and empty circles within the circle representing the winding 34 of the emitter and it is seen that brush 30 must be connec ted to the lower terminal of 9 in Order to; produce a positive unidirectional Synchr'o 'zing torque. In the Figs..2 to 9 inclusive the brushes 30, 31 are supposed to sesravaaaers coPi rest directly on the commuted winding Set; 1n practlce a commutator would, of course,. be used. The winding 9 15 shown in Fig. 2

but not in the following ones, but the circles in the following figures indicate the current distribution produced by this winding in each case.

It the phase of the, synchronizing voltage e. is allowed to differ by 90 degrees from the phase of the voltage e generated in 9 at speeds rery near the synchronous, thenlthe current introduced into 9 by conduction and derived fronrthe exciter, will produce a torque of double the slip frequency with equal positive and negative maxima. For otherwise equal conditions the maximum double frequency torque will be only half "the magnitude of the maximum strictly uni- :(lll'QCtlOnal torque and only its positive 1'm-.

pulses will be available for synchronizing" the main motor. The question might arise should c lead 0, or lag behind it by 90 degrees in order to secure the most desirable results. when 0 is in phase quadrature with e,. I

In Fig. 4 the brushes 30, 31 have been displaced by 90 elcctricaldegrees 'in the direc tion of rotation of the brushes and as compared with the-condition illustrated in Fig. 2. This is equivalent to advancing the phase of e 90 degrees withrespect to'that'of e,. For the brush position shown in Fig. 4, the synchronizing voltage and current are a maximum but-the axis of- F coincides with that of'9 and the torque is therefore zero. It

is, -however,importantto note that'this is. p the point at which the positive torquewave begins-and that the'direction in which the secondary is,magnetized by the brush voltago now coincides with that of F. InFig. 5 both F and the brushes 30, 31 have traveled through degrees in a-clockwise direction, the double frequency torque is positive and would be a maximum if the exciting flux E and the flux-F had sinusoidal distribution.

does any part of the secondary magnetizasynchronism the rotor would go into-step with9, producing a-flux of same direction as F after making up an angular displacement of zero to degrees at no-load; synchronization'could readilytake place. A movement through another 45 degrees makes the synchronizing voltage and therefore the synchronizing torque zero. A further movement of &5 degrees carries one into the re gion of the negative wave of the doublehequency'torque as shown in Fig. 6.

In Fig. 7 the brushes 30. 31 have been displaced by 90 electrical degrees against the direction of rotation of the brushes and as tion oppose 'F. It is clear that if this torque ,could accelerate the rotor, or secondary, into izs compared with Fig. 2. This is equivalentjto respect to that of 6,. Fig. 8'shows the half' way point of the negative wave of the resultmg double frequency torque. .The positive torque wave begins degrees later, when F s at right angles to the axis of the secondary winding {land the brush voltage. is zero. As theposuive torque wave grows the brush current so magnetizes the secondary that at least part 01- this magnetization opposes F, The half way point of the positive wave is shown in Fig. 9 and discloses the-fact that in order to synchronize with the right direction of excitation the rotor of the main motor would. at no-load have to make up an angular displacement of degrees instead of only zero to 90 as in Fig. 5. If synchronization does occur under the conditions of Fig. 9 it cannotbe as smooth as under the conditions of Fig. When 6 does not c0- incide in phase-with a, it should lead rather than lag behind 6,.

Turning now to the operating condition and the adjustment of the compounding characteristic, if the machine is synchronized with a strictly unidirectional torque or with 0 strictly of same phase and direction as e,,

then atv maximum load the brushes 30, 31- will possibly occupy the position shown in Fig. 3, in which case the brush voltage will be a maximum. If all or .part of the load .is thrownofi', the rotor of the main motor will momentarily accelerate, running above synchroni'sm, and will cause the differential gear to move the brushes counterclockwiseor in the direction of rotation ofvthe armas ture 34 of the exciter. Thisresiilts in a de-. magnetizing effect of the armature reaction on the excitation ofthe exciter and therefore in a diminution of the excitation of the main motor, which is as it should be if the power factor is to be kept within acceptable limits as the load decreases. But this variation of the excitation may not suitthe conditions under which the motor is to'operate; if so, then the change in excitation brought about by the movement of the brushes 30, 31 in synchronous operation and dueto the mo- 7 .nientary acceleration or deceleration of the secondary of the motor in response to varying: load can be modified by causing the brushes 30, 31 to occupy a position other than neutral, or that shown in Fig. 3, when the load on the synchronously running motor is a maximum. If the brushes are displaced against the rotation of the exciter armature then the armature reaction will assist the shunt excitation of the exci er, at maximum load and a greater movement of the brushes 3O. 31 is possible without bringing the coils undergoing commutation under the poles.- If the brushes are displaced in the opposite direction, then the armature reaction will be dcmagnctizmg even at maximum load. The,

compounding characteristic of the main motorcan be further modified by compounding BESTAVAlLABLE COP:

o r decompounding the exciter in comhination with the shifting of the brushes 30,- 31 with varying load.

The phase of the synchronizing voltage or the position of the brushes 30, 31 in normal synchronous operation can {most convenientvoltages impressed on the auxiliary mbtor 4L The phase of the synchronizing voltage can readily be so chosen that a satisfactory synchronizing-torque will be had, together with an acceptable compounding:

characteristic, without having to readjust nous speeds, thebrushes 30, 31- will revolve in the same direction'cas the armature 34 of the ex'citer. "This in no way interferesv with or modifies the adjustments to be made in order to secure the desired conformationor magnitude of the synchronizing torque, but in synchronous operation a decrease-in load.

willmove the'brushes 30, 31 against'the direction of rotation of the armature 34, thus causing the armature reaction to'assist the excitation of the exciter andproducing a. different operating characteristic. .Wh1ch ever way the brushes 30, 31 are moved out'of theneutral 'in synchronous operation, it will be understood that when the angular dis placement is large enough the brush voltage will diminish whether. the armature reaction o assists or opposestheshunt excitation of the machine. T

Instead of driving 1y be adjusted by adjusting the phase of the the shaft 26jogf thef exciter from the main motcr,-it can'be driven by a synchronous or any other .motor, in

which-case the voltage at the revolving lla brushes 30, 31 mayhaveany. desired am- I plitude even when the main motor. is at rest. Otherwise the operat onoi. the combination remains the same as when the exciter is driven by. the main. motor. In, order to :apply such a motor to the arrangement.

shown in-Fig..-1, the gear wheel 42 is. re

moved and the motor coupled to the exciter.

.The number of poles of the auxiliary motor 41 is immaterialjust'so the gears driving the brushes 30, 31 are so proportioned that they revolve synchronously with respect to the exciter when the main motor is at rest and are. at rest when the main mototrjoperate's synchronously. Crenez ally "speaking,

1,599,760 BESTAVAlLABLE COPE number of generator to the number of exciter pole pairs.- lVhen the generator is at rcst'its'slip speed is equal to its synchronous speed.

In 'cirderfto make full use of the proper ties of the improved. motor I prefer to de-.

sign. both :members without defined polar projections, using a short air-gap and well distributed windings as is usual in good induction motor practice. In that way a good starting, synchronizing and'weight efficiency are secured.

While the discussion of the various conditions governing brush displacements and other adjustments are referred to a machine With revolving secondary, and such is illustrated, it will be understood that the secondary may just as well be stationary, in which casethe primary will. revolve.

While a theory has been advanced in connection with the machine referred to herein, this has been done with a view to facilitating its description and understanding and it is to beiunderstood that I do not bindmyself to this or any other theories." I

It will be clear that various changes may without departing from the spirit of this lnvention, and it is, therefore, to'be understood that this invention is not to be limited to the specific details here shown and described. at

Having thus describedthe invention, what is claimed is: f i

1. ,A synchronous motor having aprimary member provided with a winding, a secondary member having a winding in inductive relation to said primary winding, an exciter' having afield produced by a unidirectional current and having an armature whose voltage is determined by said field, means cooperating with said armature to derive therefrom an auxiliary voltage which is of slip frequency near synchronism and unidirectional at synchronism, and means for impressing said auxiliary voltage on said secondary winding.

2. A synchronous motor having a primary member provided with a winding, a secondary member having a winding in inductive relation to said primarywinding, an exciter having a field produced by a unidirectional membeg provided with a winding, a secondary meinber having a winding in inductive relation to said primary winding, an exciter having a field produced by a unidirectional current and having an armature whose voltage is determined by said field, means cooperating with said armature for impressing on said secondary winding a voltage which is of slip frequency near synchronism and unidirectional at synchronism, means for controlling the phase of said voltage adapted to produce near synchronisni a substantially unidirectional synchronizing torque, and adapted to produce at synchronism the desired unidirectional compounding characteristic.

4. A synchronous motor; having a primary member rovided with a winding, :1 secondary mem er having a winding in inductive relation to said primary windmggan exciter having afield produced by a unidirectional current and having an armature provided with a commutator and whose voltage is determined by said field, and brushes bearing on said commutator and connected with said secondary winding and adapted to deliver a voltage which is of slip frequency near syn chronism and unidirectional at synchronism'. be made in the details of this disclosure 5. A synchronous motor having a primary member rovided with a winding, a secondary mem erhaving a windin relation to said primary winding, an exciter having a fieldproduc ed by-a unidirectional in inductive currentand havingfan armature provided 5 with a commutatorand whose voltage is determinedbysaid field, brushes bearing on.

said commutator and connected with said secondary winding and ada ted to deliver a voltage-which. is of slip requency near synchronism and unidirectional at synchronism, and means cooperating with said brushesizdapted to produce near synchro-.

nism a'osubstantially unidirectional synchronizinitorque.

6. synchronous motor having a primary J member rovided with a winding, a second ary mem errhavmga winding 1n inductive relation to said primary winding, an exciter having a field produced by a unidirectional current and. having an armature provided with a commutator and" whose voltage is determined by said field, brushes bearing on said commutator and connected with said secondary winding and adapted to deliver a voltage which is of slip frequency near synchronism and unidirectional at synchronism, and means cooperating with said brushes adaptedto control the phase of said voltage.

'7. A synchronous motor having'a primary member provided with a winding, a secondary.- member having a winding in inductive relation to sa'd primary winding, an exciter having a fiel produced by a unidirectional current and having an armature provided with a commutator and whose voltage is deiao termined by said field, brushes bearing on said commutator and connected with said secondary winding, and means for moving said brushes relatively to said commutator when the motor runs at a-speed other than the synchronous.

8. A synchronous motor having a primary member provided with a winding, a secondary member having a winding in inductive relation to said primary winding, an exciter having a field produced by unidirectional A in accordance with the departure of the motor from synchronism.

9. A synchronous motor having a primar member provided with a winding, a secon ary member having a winding in inductive relation to said primary winding, an exciter having a field produced by a unidirectional current and having an armature provided with a commutator and whose voltage is determined by said field, brushes bearing on said commutator and connected with said secondary winding, means for moving said brushes relatively to said commutator when the motor runs at a speed other than the synchronous, and means for adjusting said brushes.

10. Asynchronous motor having a primary member provided with a winding, a secondary member havmga winding in in- SESTAVAELABLE 3 3% said secondary winding, and means responsive to motor load variations for displacing said brushes relatively to the axis of the exciter field produced by said unidirectional current. v

11. A synchronous motor having a pri mary member provided with a winding, a

exciter connected to the winding on the secondary member and means for driving said brushes at a speed equal to the slip frequency of the synchronous machine multiplied by the number of pole pairs of said machine and divided by the number of pole pairs of the exciter.

. 13. A synchronous dynamo electric machine, a direct current exciter and means dependent on changes in the peripheral speed of the synchronously operating machine to.

vary the voltage or current supplied by the exclter to said synchronous mac ine.

14. A synchronous dynamo electric machine, a direct currentexciter and means deductive relation to said primary winding} pendent on changes in the peripheral speed an exciter having a field produced by a unidirectlonal current and having an armature provided with a commutator and whose voltage is determined by said field, brushes hearing on said commutator and connected, with iof the synchronously operating machine to vary the exciting flux of the exciter.

' In testimony whereof I afiix my signature this 29th. day of March, 1924. VALERE ALFRED FYNN. 

